drivers: rmnet_shs: Core conflict fix

Previously if shs had no fully idle cpus and two new flows came into SHS
and a WQ was executed between them the round robin counter would be reset
back to 0 and the two flows would not be ditributed to
different cores.

This change changes the way the wq calculates the most idle CPU  so that
new flows get distributed correctly based on least number of flows and lowest
workload across WQ ticks.

CRs-Fixed: 2503374
Change-Id: I3934b693f65579e1bd12e6f86e692f8feae2975c
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>